Great white shark

The great white shark, Carcharodon carcharias, also known as the great white, white pointer, white shark, or white death, is a species of large lamniformshark which can be found in the coastal surface waters of all the major oceans. The great white shark is mainly known for its size, with the largest individuals known to have approached or exceeded 6 m (20 ft) in length,[3] and 2,268 kg (5,000 lb) in weight.[4] This shark reaches its maturity around 15 years of age and can have a life span of over 30 years.

The great white shark came into existence during the mid-Miocene epoch. The earliest known fossils of the great white shark are about 16 million years old.[1] However, the phylogeny of the great white is still in dispute. The original hypothesis for the great white's origins is that it shares a common ancestor with a prehistoric shark, such as the C. megalodon. Similarities among the physical remains and the extreme size of both the great white and C. megalodon led many scientists to believe these sharks were closely related, and the name Carcharodon megalodon was applied to the latter. However, a new hypothesis proposes that the C. megalodon and the great white are distant relatives (albeit sharing the family Lamnidae). The great white is also more closely related to an ancient mako shark, Isurus hastalis, than to the C. megalodon, a theory that seems to be supported with the discovery of a complete set of jaws with 222 teeth and 45 vertebrae of the extinct transitional speciesCarcharodon hubbelli in 1988 and published on November 14, 2012.[11] In addition, the new hypothesis assigns C. megalodon to the genus Carcharocles, which also comprises the other megatoothed sharks; Otodus obliquus is the ancient representative of the extinct Carcharocles lineage.[12]

The great white is an epipelagic fish, observed mostly in the presence of rich game, such as fur seals, sea lions, cetaceans, other sharks, and large bony fish species. In the open ocean, it has been recorded at depths as great as 4,000 ft (1,200 m).[14] These findings challenge the traditional notion about the great white as being a coastal species.[14]

According to a recent study, California great whites have migrated to an area between Baja California and Hawaii known as the White Shark Café to spend at least 100 days before migrating back to Baja. On the journey out, they swim slowly and dive down to around 900 m (3,000 ft). After they arrive, they change behavior and do short dives to about 300 m (1,000 ft) for up to ten minutes. Another white shark that was tagged off of the South African coast swam to the southern coast of Australia and back within the year. This refuted traditional theories that white sharks are coastal territorial predators and opens up the possibility of interaction between shark populations that were previously thought to have been discrete. The reasons for their migration and what they do at their destination is still unknown. Possibilities that may support this idea include seasonal feeding or mating.[15] A similar study tracked a great white shark from South Africa swimming to Australia's northwestern coast and back, a journey of 20,000 km (12,000 mi; 11,000 nmi) in under nine months.[16]

The great white shark has a robust, large, conical snout. The upper and lower lobes on the tail fin are approximately the same size which is similar to some mackerel sharks.

A great white displays countershading, by having a white underside and a grey dorsal area (sometimes in a brown or blue shade) that gives an overall mottled appearance. The coloration makes it difficult for prey to spot the shark because it breaks up the shark's outline when seen from the side. From above, the darker shade blends with the sea and from below it exposes a minimal silhouette against the sunlight.

Great white sharks, like many other sharks, have rows of serrated teeth behind the main ones, ready to replace any that break off. When the shark bites, it shakes its head side-to-side, helping the teeth saw off large chunks of flesh.[17]

Great white shark caught off Cuba in 1945 which is allegedly 6.4 m (21 ft) long and weighing about 3,175 kg (7,000 lb).[18]

Male great whites reach maturity at 3.5–4.0 m (11–13 ft) long and females at 4.5–5.0 m (15–16 ft) long. Adults on average are 4–5.2 m (13–17.1 ft) long and have a mass of 680–1,100 kg (1,500–2,400 lb). Females are generally larger than males. The great white shark can reach 6.1 m (20 ft) in length and 1,900 kg (4,200 lb) in weight.[3] The maximum size is subject to debate because some reports are rough estimations or speculations performed under questionable circumstances.[19] Among living cartilaginous fish, only the basking and whale sharks and the manta ray average larger and heavier. These three species are generally docile in disposition and given to passively filter-feeding on very small organisms.[20]

A number of very large great white shark specimens have been recorded.[21] For decades, many ichthyological works, as well as the Guinness Book of World Records, listed two great white sharks as the largest individuals: In the 1870s, a 10.9 m (36 ft) great white captured in southern Australian waters, near Port Fairy, and a 11.3 m (37 ft) shark trapped in a herringweir in New Brunswick, Canada, in the 1930s. Some researchers question these measurements' reliability, noting they were much larger than any other accurately reported sighting. This New Brunswick shark may have been a misidentified basking shark, as the two have similar body shapes. The question of the Port Fairy shark was settled in the 1970s when J. E. Randall examined the shark's jaws and "found that the Port Fairy shark was of the order of 5 m (17 ft) in length and suggested that a mistake had been made in the original record, in 1870, of the shark's length".[22]

According to J. E. Randall, the largest white shark reliably measured was a 6.0 m (19.7 ft) individual reported from Ledge Point, Western Australia in 1987.[22] Another great white specimen of similar size has been verified by the Canadian Shark Research Center: A female caught by David McKendrick of Alberton, Prince Edward Island, in August 1988 in the Gulf of St. Lawrence off Prince Edward Island. This female great white was 6.1 m (20 ft) long.[3] However, there is a report considered reliable by some experts of a larger great white shark specimen from Cuba in 1945. This specimen was 6.4 m (21 ft) long and had a body mass of about 3,324 kg (7,330 lb).[23][24]

Great white shark caught off Hualien County, Taiwan, on May 14, 1997: It was reportedly almost 7 m (23 ft) in length with a mass of 2,500 kg (5,500 lb).[21]

Several great white sharks caught in modern times have been estimated to be more than 7 m (23 ft) long,[25] but these claims have received some criticism.[19][25] However, J. E. Randall believed that great white shark may have exceeded 6.1 m (20 ft) in length.[22] A great white shark was captured near Kangaroo Island in Australia on April 1, 1987. This shark was estimated to be more than 7 m (23 ft) long by Peter Resiley,[22][26] and has been designated as KANGA.[25] Another great white shark was caught in Malta by Alfredo Cutajar on April 16, 1987. This shark was also estimated to be around 7.13 m (23.4 ft) long by John Abela and has been designated as MALTA.[25] However, Cappo drew criticism because he used shark size estimation methods proposed by J. E. Randall to suggest that the KANGA specimen was 5.8–6.4 m (19–21 ft) long.[25] In a similar fashion, I. K. Fergusson also used shark size estimation methods proposed by J. E. Randall to suggest that the MALTA specimen was 5.3–5.7 m (17–19 ft) long.[25] However, photographic evidence suggested that these specimens were larger than the size estimations yielded through Randall's methods.[25] Thus, a team of scientists—H. F. Mollet, G. M. Cailliet, A. P. Klimley, D. A. Ebert, A. D. Testi, and L. J. V. Compagno—reviewed the cases of the KANGA and MALTA specimens in 1996 to resolve the dispute by conducting a comprehensive morphometric analysis of the remains of these sharks and re-examination of photographic evidence in an attempt to validate the original size estimations and their findings were consistent with them. The findings indicated that estimations by P. Resiley and J. Abela are reasonable and could not be ruled out.[25]

Great white shark's skeleton

One contender in maximum size is the tiger shark, Galeocerdo cuvier. While tiger sharks which are typically both a few feet smaller and have a leaner, less heavy body structure than white sharks, have been confirmed to reach at least 5.5 metres (18 ft) in the length, an unverified specimen was reported to have measured 7.4 metres (24 ft) in length and weighed 3,110 kilograms (6,900 lb).[20][27] Some other macropredatory sharks such as the Greenland shark, Somniosus microcephalus, and the Pacific sleeper shark, Somniosus pacificus, are also reported to rival these sharks in length (but probably weigh a bit less since they more slender in build than a great white) in exceptional cases.[28][29] The question of maximum weight is complicated by the unresolved question of whether or not to include the shark's stomach contents when weighing the shark. With a single bite a great white can take in up to 14 kg (31 lb) of flesh, and can also consume several hundred kilograms of food.

The largest great white recognized by the International Game Fish Association (IGFA) is one caught by Alf Dean in the south Australian waters in 1959, weighing 1,208 kg (2,660 lb).[19] Several larger great whites caught by anglers have since been verified, but were later disallowed from formal recognition by IGFA monitors for rules violations.

Great white sharks, like all other sharks, have an extra sense given by the Ampullae of Lorenzini which enables them to detect the electromagnetic field emitted by the movement of living animals. Every time a living creature moves, it generates an electrical field and great whites are so sensitive they can detect half a billionth of a volt. Even heart beats emit a very faint electrical pulse. If it is close enough, the shark can detect even that faint electrical pulse. Most fish have a less-developed but similar sense using their body's lateral line.[30]

To more successfully hunt fast and agile prey such as sea lions, the great white has adapted to maintain a body temperature warmer than the surrounding water. One of these adaptations is a "rete mirabile" (Latin for "wonderful net"). This close web-like structure of veins and arteries, located along each lateral side of the shark, conserves heat by warming the cooler arterial blood with the venous blood that has been warmed by the working muscles. This keeps certain parts of the body (particularly the stomach) at temperatures up to 14 °C (25 °F)[31] above that of the surrounding water, while the heart and gills remain at sea temperature. When conserving energy the core body temperature can drop to match the surroundings. A great white shark's success in raising its core temperature is an example of gigantothermy. Therefore, the great white shark can be considered an endothermicpoikilotherm because its body temperature is not constant but is internally regulated.[17]

A 2007 study from the University of New South Wales in Sydney, Australia, used CT scans of a shark's skull and computer models to measure the shark's maximum bite force. The study reveals the forces and behaviors its skull is adapted to handle and resolves competing theories about its feeding behavior.[32] In 2008, a team of scientists led by Stephen Wroe conducted an experiment to determine the great white shark's jaw power and findings indicated that a specimen more than 6.1 m (20 ft) long could exert a bite force of over 18,000 newtons (4,000 lbf).[24]

This shark's behavior and social structure is not well understood. In South Africa, white sharks have a dominance hierarchy depending on the size, sex and squatter's rights: Females dominate males, larger sharks dominate smaller sharks, and residents dominate newcomers. When hunting, great whites tend to separate and resolve conflicts with rituals and displays. White sharks rarely resort to combat although some individuals have been found with bite marks that match those of other white sharks. This suggests that when another shark approaches too closely to another great white, they react with a warning bite. Another possibility is that white sharks bite to show their dominance.

The great white shark is one of only a few sharks known to regularly lift its head above the sea surface to gaze at other objects such as prey. This is known as spy-hopping. This behavior has also been seen in at least one group of blacktip reef sharks, but this might be learned from interaction with humans (it is theorized that the shark may also be able to smell better this way because smell travels through air faster than through water). The white sharks are generally very curious animals, display intelligence and may also turn to socializing if the situation demands it. At Seal Island, white sharks have been observed arriving and departing in stable "clans" of two to six individuals on a yearly basis. Whether clan members are related is unknown but they get along peacefully enough. In fact, the social structure of a clan is probably most aptly compared to that of a wolf pack; in that each member has a clearly established rank and each clan has an alpha leader. When members of different clans meet, they establish social rank nonviolently through any of a fascinating variety of interactions.[33]

The great white shark's reputation as a ferocious predator is well-earned, yet they are not (as was once believed) indiscriminate "eating machines". They are ambush hunters, taking prey by surprise from below. Near Seal Island, in South Africa's False Bay, shark attacks most often occur in the morning, within 2 hours after sunrise, when visibility is poor. Their success rate is 55% in the first 2 hours, falling to 40% in late morning after which hunting stops.[33]

Hunting techniques vary by species of the prey. Off Seal Island, the sharks ambush brown fur seals from below at high speeds, hitting the seal mid-body. They go so fast that they can completely leave the water. The peak burst speed of these sharks is largely accepted in the scientific community to be above 40 kilometres per hour (25 mph). However further precision is still speculative.[37] They have also been observed chasing prey after a missed attack. Prey is usually attacked at the surface.[38]

Off California, sharks immobilize northern elephant seals with a large bite to the hindquarters (which is the main source of the seal's mobility) and wait for the seal to bleed to death. This technique is especially used on adult male elephant seals which can be as large or larger than the hunter and are potentially dangerous adversaries. Prey is normally attacked sub-surface. Harbour seals are taken from the surface and dragged down until they stop struggling. They are then eaten near the bottom. California sea lions are ambushed from below and struck mid-body before being dragged and eaten.[39]

A beachcomber looking at bite marks on a beached whale from a great white shark

Even though the great whites are known to generally avoid conflicts with each other, the phenomenon of cannibalism is not alien to this species. Large individuals may aggressively interact intraspecifically with small individuals. A 3 m (9.8 ft) long great white shark was nearly bitten into two by a reportedly 6 m (20 ft) long great white shark in Stradbroke Island, near Brisbane in Australia.[42]

White sharks also scavenge on whale carcasses. In one such documented incident, white sharks were observed scavenging on a whale carcass alongside tiger sharks.[43]

Almost nothing is known about reproduction in great whites. Some evidence points to the near-soporific effect of a large feast (such as a whale carcass) possibly inducing mating.[44] Great white sharks also reach sexual maturity at around 15 years of age.[45] Maximum life span is believed to be more than 30 years (see references).

Little is known about the great white shark's behavior in the way of mating habits. Birth has never been observed, but pregnant females have been examined. Great white sharks are ovoviviparous, which means eggs develop and hatch in the uterus and continue to develop until birth.[46] The great white has an 11-month gestation period. The shark pup's powerful jaws begin to develop in the first month. The unborn sharks participate in oophagy, in which they feed on ova produced by the mother. Delivery is in spring and summer.[47]

A breach is the result of a high speed approach to the surface with the resulting momentum taking the shark partially or completely clear of the water. This is a hunting technique employed by great white sharks whilst hunting seals. This behavior often takes place on cape fur seals at Seal Island in False Bay, South Africa but due to the randomness of the location of a shark's breach, it was very hard to document. It was first photographed by Chris Fallows and Rob Lawrence who developed the technique of towing a slow moving seal decoy to trick the sharks to breach.[48] Here, in the region of 600 natural predatory events are recorded annually from April to September each year. The seals swim on the surface and the great white sharks launch their predatory attack from the deeper water below. They can reach speeds of up to 40 kilometres per hour (25 mph) and can at times launch themselves more than 10 feet (3.0 m) into the air. Data recorded shows that the sharks are successful in just under 50% of all these natural predatory events.[49] In 2011, a 3 metres (9.8 ft) long shark jumped onto a seven-person research vessel off Seal Island in Mossel Bay. The crew were undertaking a population study using sardines as bait, and the incident was judged to be an accident.[50]

More than any documented attack, Peter Benchley's best selling novel Jaws and the subsequent 1975 film adaptation directed by Steven Spielberg provided the great white shark with the image of being a "man eater" in the public mind.[51] While great white sharks have killed humans, they typically do not target them: for example, in the Mediterranean Sea there have been 31 confirmed attacks against humans in the last two centuries, most of which were non-fatal. Many of the incidents seemed to be "test-bites". Great white sharks also test-bite buoys, flotsam, and other unfamiliar objects, and they might grab a human or a surfboard to identify what it is.

The great white shark is one of only four kinds of sharks that have been involved in a significant number of fatal unprovoked attacks on humans.

Other incidents seem to be cases of mistaken identity, in which a shark ambushes a bather or surfer from below, believing the silhouette is from a seal. Many attacks occur in waters with low visibility or other situations which impair the shark's senses. The species appears to not like the taste of humans, or at least finds the taste unfamiliar. Further research shows that they can tell in one bite whether or not the object is worth attacking. Humans, for the most part, are too bony for their liking. They much prefer a fat, protein-rich seal.[52]

However, some researchers have hypothesized that the reason the proportion of fatalities is low is not because sharks do not like human flesh, but because humans are often able to escape after the first bite. In the 1980s John McCosker, the Chair of Aquatic Biology at California Academy, noted that divers who dove solo and were attacked by great whites were generally at least partially consumed, while divers who followed the buddy system were generally rescued by their buddy. McCosker and Timothy C. Tricas, an author and professor at the University of Hawaii, suggest that a standard pattern for great whites is to make an initial devastating attack and then wait for the prey to weaken before consuming the wounded animal. Humans' ability to move out of reach with the help of others, thus foiling the attack, is unusual for a great white's prey.[53]

Humans are not appropriate prey because the shark's digestion is too slow to cope with a human's high ratio of bone to muscle and fat. Accordingly, in most recorded attacks, great whites broke off contact after the first bite. Fatalities are usually caused by blood loss from the initial bite rather than from critical organ loss or from whole consumption. Since 1990, there have been a total of 139 unprovoked great white shark attacks, 29 fatal.[54]

A shark conservationist, Jimmy Hall, reported and documented his personal encounter with a very large great white shark, nicknamed Schatzi, in December 2005 in waters off Hawaii. This encounter received worldwide attention as it remained entirely peaceful. J. Hall was at first cautious, but later swam with this shark without cage protection and touched it repeatedly while filming it simultaneously.[55]

Great white sharks infrequently attack and sometimes even sink boats. Only five of the 108 authenticated unprovoked shark attacks reported from the Pacific Coast during the 20th century involved kayakers.[60] In a few cases they have attacked boats up to 10 metres (33 ft) in length. They have bumped or knocked people overboard, usually attacking the boat from the stern. In one case in 1936, a large shark leapt completely into the South African fishing boat Lucky Jim, knocking a crewman into the sea. Tricas and McCosker's underwater observations suggest that sharks are attracted to boats due to the electrical fields they generate.[61]

Prior to August 1981, no great white shark in captivity lived longer than 11 days. In August 1981, a white shark survived for 16 days at SeaWorldSan Diego before being released.[62] The idea of containing a live great white at SeaWorldOrlando was used in the 1983 film Jaws 3-D.

In 1984, shortly before its opening day, the Monterey Bay Aquarium in Monterey, California, housed its first great white shark which had died after 10 days. In July 2003, Monterey researchers captured a small female and kept it in a large netted pen near Malibu for five days. They had the rare success of getting the shark to feed in captivity before its release.[63] Not until September 2004 was the aquarium able to place a great white on long-term exhibit. A young female, which was caught off the coast of Ventura, was kept in the aquarium's massive 3,800,000-litre (1,000,000 US gal) Outer Bay exhibit for 198 days before she was released in March 2005. She was tracked for 30 days after release.[64] On the evening of August 31, 2006, the aquarium introduced a juvenile male caught outside Santa Monica Bay.[65] His first meal as a captive was a large salmon steak on September 8, 2006, and as of that date, he was estimated to be 1.72 metres (68 in) in length and to weigh approximately 47 kilograms (100 lb). He was released on January 16, 2007, after 137 days in captivity.

In addition, Monterey Bay Aquarium housed a third great white, a juvenile male, for 162 days between August 27, 2007, and February 5, 2008. On arrival, he was 1.4 metres (4 ft 7 in) long and weighed 30.6 kilograms (67 lb). He grew to 1.8 metres (5 ft 11 in) and 64 kilograms (140 lb) before release. A juvenile female came to the Outer Bay Exhibit on August 27, 2008. While she did swim well, the shark fed only one time during her stay and was tagged and released on September 7, 2008. Another juvenile female was captured near Malibu on August 12, 2009, introduced to the Outer Bay exhibit on August 26, 2009, and was successfully released into the wild on November 4, 2009.[66] The Monterey Bay Aquarium recently added a 4.58 feet (1.40 m) long male into their redesigned "Open Sea" exhibit on August 31, 2011. The animal was harvested in the waters off of Malibu.

Cage diving is most common at sites where great whites are frequent including the coast of South Africa, the Neptune Islands in South Australia,[68] and Guadalupe Island in Baja California. Cage diving and swimming with sharks is a focus for a booming tourist industry due to its popularity.[69][70] A common practice is to chum the water with pieces of fish to attract the sharks. These practices may make sharks more accustomed to people in their environment and to associate human activity with food; a potentially dangerous situation. By drawing bait on a wire towards the cage, tour operators lure the shark to the cage, possibly striking it, exacerbating this problem. Other operators draw the bait away from the cage, causing the shark to swim past the divers.

At present, hang baits are illegal off Isla Guadalupe and reputable dive operators do not use them. Operators in South Africa and Australia continue to use hang baits and pinniped decoys.[71]

Companies object to being blamed for shark attacks, pointing out that lightning tends to strike humans more often than sharks bite humans.[72] Their position is that further research needs to be done before banning practices such as chumming, which may alter natural behavior.[73] One compromise is to only use chum in areas where whites actively patrol anyway, well away from human leisure areas. Also, responsible dive operators do not feed sharks. Only sharks that are willing to scavenge follow the chum trail and if they find no food at the end then the shark soon swims off and does not associate chum with a meal. It has been suggested that government licensing strategies may help enforce these suggested advisories.[71]

The shark tourist industry has some financial leverage in conserving this animal. A single set of great white jaws can fetch a one-time price of up to £20,000. However, that is a fraction of the tourism value of a live shark, a more sustainable economic activity. For example, the dive industry in Gansbaai, South Africa, consists of six boat operators with each boat guiding 30 people each day. With fees between £50 to £150 per person, a single live shark that visits each boat can create anywhere between £9,000 and £27,000 of revenue daily.[74]

It is unclear how much of a concurrent increase in fishing for great white sharks has caused the decline of great white shark populations from the 1970s to the present. No accurate population numbers are available, but the great white shark is now considered vulnerable.[2] Sharks taken during the long interval between birth and sexual maturity never reproduce, preventing population recovery.

The IUCN notes that very little is known about the actual status of the great white shark, but as it appears uncommon compared to other widely distributed species, it is considered vulnerable.[2] It is included in Appendix II of CITES,[8] meaning that international trade in the species requires a permit.[75] As of March 2010, it has also been included in Annex I of the CMSMigratory Sharks MoU, which strives for increased international understanding and coordination for the protection of certain migratory sharks.[76]

Fishermen target many sharks for their jaws, teeth, and fins, and as game fish in general. The great white shark, however, is rarely an object of commercial fishing, although its flesh is considered valuable. If casually captured (it happens for example in some tonnare in the Mediterranean), it is misleadingly sold as smooth-hound shark.

As of April 2007, great white sharks were fully protected within 370 kilometres (200 nmi) of New Zealand and additionally from fishing by New Zealand-flagged boats outside this range. The maximum penalty is a $250,000 fine and up to six months in prison.[77] In 2013, great white sharks were added to California's Endangered Species Act. From data collected, the population of great whites in the North Pacific is estimated to be fewer than 340 individuals. Research also reveals these sharks are genetically distinct from other members of their species elsewhere in Africa, Australia, and the east coast of North America, having been isolated from other populations. [78] Australia's population of great whites was revealed in a study published on July 7, 2012 was revealed to be two separate populations separated by the Bass Strait into eastern and western populations, and may require regional protection. [79]

Although the great white is typically regarded as an apex predator in the wild, it is in rare cases preyed upon by the larger orca (also known as the killer whale). Interspecific competition between the great white shark and the orca is probable in regions where dietary preferences of both species may overlap.[40] An incident was documented on October 4, 1997, in the Farallon Islands off California in the United States. An estimated 4.7–5.3-metre (15–17 ft) female orca immobilized an estimated 3–4-metre (9.8–13 ft) great white shark.[80] The orca held the shark upside down to induce tonic immobility and kept the shark still for fifteen minutes, causing it to suffocate and then proceeded to eat the dead shark's liver.[40][80][81] It is believed that the scent of the slain shark's carcass caused all the great whites in the region to flee, forfeiting an opportunity for a great seasonal feed.[82] Another similar attack apparently occurred there in 2000, but its outcome is not clear.[83] After both attacks, the local population of about 100 great whites vanished.[81][83] Following the 2000 incident, a great white with a satellite tag was found to have immediately submerged to a depth of 500 m (1,600 ft) and swum to Hawaii.[83]

^Rice, Xan (2011-07-19). "Great white shark jumps from sea into research boat". The Guardian (London: Guardian Media Group). Retrieved 2011-07-20. "Marine researchers in South Africa had a narrow escape after a three-metre-long great white shark breached the surface of the sea and leapt into their boat, becoming trapped on deck for more than an hour. [...] Enrico Gennari, an expert on great white sharks, [...] said it was almost certainly an accident rather than an attack on the boat."

^Benchley, Peter (April 2000). "Great white sharks". National Geographic: 12. ISSN00279358. "considering the knowledge accumulated about sharks in the last 25 years, I couldn't possibly write Jaws today ... not in good conscience anyway ... back then, it was OK to demonize an animal."